1. Field of the Invention
The present invention relates to 1,4-dihydropyridine derivatives having the increasing activity of the cytotoxity of anticancer agents in the drug-resistant cancer.
2. Description of the Prior Art
As 1,4-dihydropyridine derivatives having the increasing activity of the cytotoxity of anticancer agents in the drug-resistant cancer, there have been known nicardipine and the like in the past [T. Tsuruo et al., Cancer Res., vol. 43, page 2905 (1983)].
The present inventors have found that 1,4dihydropyridine derivatives having the carboxyl groups to which specific groups are introduced enhance the therapeutic effect of anticancer agents with low side-effect, and have accomplished the present invention.